The definition of "natural" behavioral capacities and the interaction of the genetic substratum with developmental events in the production of species typical behavior continues to occupy scientific attention and to elude our understanding. After more than a century of documentation of the remarkable behavioral similarities of MZ twins reared apart, we continue to collect additional data, as in the case of the current Bouchard studies of MZ twins reared in different cultures, and to be amazed by the overweening effect of the genome while, at the same time, resisting the ideal of genetic determism in the behavioral realm. Ethologists have emphasized species specific-behaviors describable as sequences of motor patterns and understandable in terms of teleologic notions of adaptive value. Sociobiologists have developed a simple numerical concept of genetic relationships contributing to group survival, but eschewing group selection and begging the question of the lack of any 1:1 relationship between genotype and phenotype. Our concern is with the problems of how genes act in the production of behavioral phenotypes. The genus Canis, which can be freely interbred, and which offers a broad spectrum of genetically based behaviors, provides an opportunity for such analyses. Species having different phenotypes for the same behavior can be crossed and the factors influencing gene expression can be studied in hybrids possessing both genetic systems, which, by their nature, cannot be expressed simultaneously. The present study seeks to identify two such systems in coyote X dog hybrids and to characterize these as models for further behavior genetic analyses in the course of a year.